1. Field of the Invention
This invention relates generally to methods of making magnetic heads, and more particularly to methods of making magnetic heads with improved contiguous junctions by reducing the size of the lift-off mask after ion milling the sensor materials and before depositing the hard bias and lead layers.
2. Description of the Related Art
Magnetic head assemblies are typically made of multiple thin film layers which are patterned to form various shaped layers in the head. Some of the layers are plated while other layers are sputter deposited on a wafer substrate. The read head portion of a magnetic head assembly includes multiple layers that are typically sputter deposited. For example, the multiple layers of a read sensor, hard bias and lead layers connected to the read sensor, and first and second read gap layers below and on top of the read sensor are typically sputter deposited.
One prior art method of forming shaped sputter deposited layers is to sputter deposit a full film layer of the required material on a wafer substrate, form a patterned photoresist layer on the layer, ion mill away the exposed portion of the layer, deposit hard bias and lead layers, and remove the photoresist layer to thereby leave the desired shaped layer that was protected therebelow. This first conventional method of shaping sputter deposited layers has been generally superseded by a second conventional method which utilizes a bilayer lift-off mask scheme.
The bilayer lift-off mask used in the second conventional method has a T-shape (as seen in cross-section) wherein the vertical portion of the T is short and wide but less wide than the horizontal top portion of the T. The top portion of the T is generally a patterned photoresist layer and the bottom vertical portion of the T is a release layer. This configuration provides first and second undercuts (as seen in cross-section) wherein each undercut has a height and a length below the top photoresist portion. In this method, the bilayer lift-off mask is employed for the purpose of making contiguous junctions of the first and second hard bias/lead layers with first and second side edges respectively of the read sensor.
More particularly, multiple read sensor layers are sputter deposited in full film on the wafer substrate followed by formation of the bilayer lift-off mask covering a read sensor site. Ion milling is then employed to remove all of the read sensor material except that below the mask. Full films of hard bias and lead layer materials are then sputter deposited which cover the top of the lift-off mask and an area surrounding the lift-off mask. Typically, it is important that the height and length of the undercuts is sufficient such that a photoresist stripper can reach the bottom release layer. The stripper is then introduced to dissolve the bottom release layer after the hard bias and lead layer depositions. This causes the bilayer lift-off mask and the hard bias and lead materials deposited thereon to be released from the wafer substrate leaving the aforementioned contiguous junctions between the first and second hard bias/lead layers and the first and second side edges respectively of the read sensor.
The bilayer lift-off mask scheme significantly improves the making of read heads by forming contiguous junctions between the hard bias/lead layers and the read sensor. Fewer processing steps are required and the profile of the lead and hard bias layers above the read sensor has been reduced. Unfortunately, however, many bilayer lift-off masks using this conventional methodology are better suited for the construction of read heads with a track width of greater than approximately 0.2 microns. The more narrow the track width, the greater the tracks per inch (TPI) that can be read by the read head from a rotating magnetic disk. Accordingly, the greater the tracks per inch the greater the storage capacity of a disk drive employing such a read head.
The bi-layer lift-off mask is made using commercially available photoresists which are relatively thick (e.g. thicker than 3000 Angstroms). Such a thick photoresist layer causes shadowing where the thickness of the hard bias layers in the contiguous junction region is less than optimal. Also, the relatively large width of the photoresist causes the sensor coverage by the hard bias and lead layers to be less than ideal. Thus, it would be advantageous if the hard bias thickness were increased in the junction region and the conductive leads were deposited further over the edges of the read sensor. If this were the case, the stability and the transfer curve of the read sensor would be improved.
Variations of the lift-off mask scheme have improved the formation of the read sensor and solved some of these problems to a limited extent. For example, the “lead overlay” design provides for reduced track widths, but requires process alignments that are critical to the resulting structure, as well as multiple photoresist processes.
Accordingly, there is a strong-felt need for improved methods of forming read sensors with improved contiguous junctions. Methods that do not require critical alignments and more than one photoresist processes are preferable.